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Biomedical subjects

R C Rowe

Publications and source records attributed to R C Rowe.

13 recordsLinked to original sources
PubMed1979

The mechanical strength of film-coated tablets.

The mechanical strength of film-coated tablets has been assessed using the diametral compression test. The results show that the influence of the film is more complex than that suggested by Stern (1976). The film may increase the breaking load of the core itself by acting as a padding material during the test and also by filling in surface irregularities. The film may also have enough intrinsic strength and elasticity to hold the core together once it has broken. The maximum breaking load to completely fracture the coated tablet is related to film properties, but the relation is not a simple one.

Hardness↗
PubMed1979

Plasticization of cellulose ethers used in the film coating of tablets.

Plasticizer/polymer interactions have been studied by measuring the intrinsic viscosities of both ethyl cellulose and hydroxypropyl methylcellulose in a series of dialkyl phthalates and in a series of liquid glycols respectively. A correlation was found between the intrinsic viscosity of the polymer/plasticizer solutions and the tensile strength, elongation at rupture and work done in stressing to failure of cast films--the mechanical properties being at a minimum when the intrinsic viscosity was at a maximum. This correlation held only within a homologous series of plasticizers and none was found for plasticizers of different structures. A relationship was found between the lowering of a calculated glass transition temperature of hydroxypropyl methylcellulose in the presence of the plasticizers propylene glycol, polyethylene glycol 200 and glycerol and the intrinsic viscosity of the corresponding solutions--the higher the viscosity the greater the lowering of the transition temperature.

Cellulose↗
PubMed1978

The measurement of the adhesion of film coatings to tablet surfaces: the effect of tablet porosity, surface roughness and film thickness.

The effect of tablet porosity, surface roughness and film thickness on the adhesion of hydroxypropyl methyl cellulose films to placebo tablet substrates have been studied using a specially designed tensile tester (Fisher & Rowe, 4976). There were direct relations between measured adhesion and tablet porosity and also surface roughness and tablet porosity. The effect of film thickness on the measured adhesion is complex with an initial decrease with thicknesses up to 35 micron and then a gradual increase with thicknesses up to 140 micron dut to differences in the strees distribution within the film during testing. A knowledge of these effects is necessary if results from various sources are to be compared. The findings illustrate the potential capability of the extrapolation of measured adhesion results to zero porosity and zero thickness values in order to obtain a measure of the true or intrinsic adhesion at any film/tablet interface without the confusing elements of tablet porosity, surface roughness and residual stresses in the film.

Adhesiveness↗
PubMed1978

The effect of some formulation and process variables on the surface roughness of film-coated tablets.

The effect of some formulation and process variables on the surface appearance of film-coated tablets has been examined by measuring the arithmetic mean roughness, Ra, values across the faces of tablets before and after they were coated with hydroxypropyl methyl-cellulose. For all tablet cores except those that were very porous, film coating resulted in an increasing surface roughness; for very porous cores a decrease was found. Tablets with rough surfaces were produced by coating with low molecular weight grades of the polymer; increasing the polymer molecular weight resulted in a smoother finish with a minimum roughness at intermediate molecular weight grades. Increasing the polymer concentration above 2% w/v caused an increase in roughness as did increasing film thickness to 140 micrometer. There was a minimum in roughness at film thickness of 20 micrometer. The addition of pigment in low concentrations (0--25% v/v) caused a marginal increase in surface roughness but at concentrations above the critical pigment volume concentration, the surfaces were very rough. The results illustrate the potential of the method in the optimization of film formulations and process conditions during product development.

Cellulose↗
PubMed1977

The adhesion of film coatings to tablet surfaces--the effect of some direct compression excipients and lubricants.

The effect of some direct compression excipients and lubricants on the adhesion of hydroxypropyl methyl cellulose films has been examined using a specially designed tensile testing apparatus (Fisher & Rowe, 1976). The adhesion was found to be influenced by both the roughness, including microporosity, of the tablet surface and its polarity. Tablets prepared from microcrystalline cellulose showed very high adhesions despite having relatively smooth surfaces, owing to the surface being saturated with hydroxyl groups able to form hydrogen bonds with the corresponding groups on the polymer. The addition of magnesium or calcium stearate to the tablet was found to decrease the adhesion, but the addition of stearic acid caused a significant increase. The effect of lubricant concentration on the adhesion could be expressed by an equation similar to that proposed by Hofrichter & McLaren (1948) for the adhesion of vinyl chloride/vinyl acetate copolymers to regenerated cellulose.

Adhesiveness↗
PubMed1976

The adhesion of film coatings to tablet surfaces--instrumentation and preliminary evaluation.

The strength of the adhesive bond between a film coating and a tablet surface has been studied using a specially designed tensile testing apparatus. The adhesion has been taken as the force required to remove the film from unit area of the tablet surface and has been shown to be dependent on the compression pressure used to prepare the tablet and on changes in the film formulation. Although plasticizers did not show any significant effect on the adhesion of a hydroxypropyl methylcellulose film, a reduction of 45% was found on the addition of 10% w/w titanium dioxide.

Adhesiveness↗